This invention relates generally to laminar flow high speed aircraft wing configurations adapted for efficient operations at high subsonic speeds and lower supersonic speeds and (or generally, transonic speeds). We have found that the low sweep thin laminar flow wing type originally intended for efficient supersonic cruise also has, with minor variations, excellent performance at transonic speeds. Accordingly, just as for the efficient supersonic laminar flow wing, several improvements are useful both at design cruise condition, as well as at the lower speeds required during takeoff and landing. More specifically it concerns improvements in the following configuration areas:
a) strake,
b) raked wing tip,
c) reversed fillet wing-strake junction,
d) inboard leading edge flap,
e) hybrid plain-split flap system.
Prior Richard Tracy U.S. patents disclose a laminar flow wing for efficient supersonic flight (U.S. Pat. No. 5,322,242, U.S. Pat. No. 5,518,204, U.S. Pat. No. 5,897,076 and U.S. Pat. No. 6,149,101). A subsequent Richard Tracy et al U.S. Pat. No. 7,000,870 discloses similar wing designs for efficient flight at transonic speeds. These are somewhat thicket than the supersonic laminar flow wing in terms of the ratio of maximum thickness to chord, but are of similar type, having generally biconvex airfoils, relatively low sweep, and a sharp or slightly blunted leading edge. They also have similar characteristics at the low speeds and higher angles of attack associated with landing and takeoff. Thus aircraft with this type of transonic laminar flow wing benefit from improvements similar to those disclosed for the supersonic laminar flow wing in the patent application Ser. No. 11/975,802 of which this is a continuation in part.
The areas of improvement, which principally benefit the low speed characteristics of aircraft using the wing, are enumerated above (a through e). The wing described in the prior Tracy patents has a sharp, modified biconvex airfoil, with less than about 30° leading edge sweep in order to maintain an attached shock at supersonic cruise conditions, and thickness-chord ratio (t/c) of about 2% (or 3% for the transonic wing) as a span-wise average over the majority of the outer portion of the wing. The latter excludes a zone near the inboard end, which may be thicker, up to about 4% t/c (or more for the transonic wing) in combination with fuselage area ruling.
There are several unique characteristics of the supersonic and transonic laminar flow wing which pose challenges, especially in low speed flight. These include (1) its sharp or slightly blunted leading edge which causes a separation “bubble” at almost any angle of attack in subsonic flight, (2) its extremely thin airfoil which imposes a structural weight penalty as aspect ratio is increased, and (3) the un-swept leading edge which limits the effectiveness of “area ruling” of the body to minimize transonic wave drag. These (and other characteristics) are unique to the supersonic laminar wing and are substantially mitigated by the herein claimed improvements, acting individually or together, in combination with this type of wing.